Abstract
Geothermal power is being regarded as depending on techniques derived from hydrocarbon production in worldwide current strategy. However, it has artificially been developed far less than its natural potentials due to technical restrictions. This paper introduces the Enhanced Geothermal System based on Excavation (EGS-E), which is an innovative scheme of geothermal energy extraction. Then, based on cohesion-weakening-friction-strengthening model (CWFS) and literature investigation of granite test at high temperature, the initiation, propagation of excavation damaged zones (EDZs) under unloading and the EDZs scale in EGS-E closed to hydrostatic pressure state is studied. Finally, we have a discussion about the further evolution of surrounding rock stress and EDZs during ventilation is studied by thermal-mechanical coupling. The results show that the influence of high temperature damage on the mechanical parameters of granite should be considered; Lateral pressure coefficient affects the fracture morphology and scale of tunnel surrounding rock, and EDZs area is larger when the lateral pressure coefficient is 1.0 or 1.2; Ventilation of high temperature and high in-situ stress tunnel have a significant effect on the EDZs scale; Additional tensile stress is generated in the shallow of tunnel surrounding rock, and the compressive stress concentration transfers to the deep. EDZs experiences three expansion stages of slow, rapid and deceleration with cooling time, and the thermal insulation layer prolongs the slow growth stage.
Highlights
Geothermal resources have become a key research and development objective among the world’s renewable clean energy options because of its source stability, potential high utilization ratio, tremendous reserve and widespread distribution [1]
Once large-scale utilization was realized, geothermal energy would act as a key technique to cope with the environmental problems brought from mainly consuming fossil fuels
To be frank, EGS-D has to date been failing to be successfully commercialized
Summary
Geothermal resources have become a key research and development objective among the world’s renewable clean energy options because of its source stability, potential high utilization ratio, tremendous reserve and widespread distribution [1]. The problem of deep rock excavation engineering, especially the EGS-E engineering, has two main characteristics simultaneously: high in-situ stress and high temperature conditions For the former, many researchers studied the stress redistribution and damage extent of surrounding rock due to excavation by relying on empirical approach [17], numerical simulation [18,19] and theoretical calculation [20]. For the latter, relevant studies focused on the temperature evolution of surrounding rock [21], effective ventilation distance [22] and heat insulation [23] in tunnel ventilation. The further evolution law of damage caused by tunnel ventilation after surrounding rock damage was studied
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